Diagnosis of porphyric syndromes: a practical approach in the era of molecular biology.

For cost-effective diagnosis of porphyric syndromes, a logical stepwise approach is best. If neurovisceral features suggest an acute porphyric syndrome, a rapid screening test for urinary porphobilinogen should be performed. If clinical features suggest a cutaneous porphyria, then for solar urticaria and acute photosensitivity (suggesting protoporphyria) screening tests for increased erythrocytic porphyrins should be done; for vesiculobullous formation (suggesting porphyria cutanea tarda, hereditary coproporphyria, or variegate porphyria) a screening test for urinary porphyrins should be done. Positive screening tests should be confirmed with targeted quantitative testing. Enzymatic assays and DNA-based testing are not usually needed for rapid diagnosis or management of symptomatic subjects, but they are useful for kindred evaluation and genetic counseling.